Measuring international migration across countries is complex. The lack of quality in available migration data has repercussions on the estimates of migration flows and stocks. Nevertheless, Bayesian methodologies have been used in complementing in-flows and out-flows of migrants from European countries to estimate the true flow of migrants. The same framework has been used for combining multiple surveys in the UK. We want to use this Bayesian framework to study the true stock of migrants in the UK. We aim to complement the Annual Population Survey with data from Facebook Advertising Platform. The advantage of this model is that it considers the limitations of the datasets and provides probability distributions to model the issue. We are exploring whether combining survey data with digital data might help in providing a more up-to-date picture of migrations stocks within one country.